The stressed panel fastener of U.S. Pat. No. 3,192,980 has proved very successful for uses such as the retention of the panels of aircraft. This is a self-locking captive fastener that provides good resistance to shear loads. However, this fastener suffers from the drawback of being relatively complex and of expensive machined construction. It is also more bulky and heavier than desired. The nut of the fastener of the aforementioned patent is held to one workpiece by a split annular resilient ring that bears against the cylindrical surface of the nut and can enter a groove near the outer end of the nut when the nut is loosened. In the latter position, the ring prevents withdrawal of the nut from the opening in the workpiece. However, such an exposed retainer ring is relatively easily dislodged from the nut so that its function is lost. Even more serious, the loose retainer ring can cause considerable damage such as, for example, when falling into the intake of a jet engine.
In the designs of U.S. Pat. Nos. 3,289,726 and 3,765,465, grommets were added to receive the outer portions of the retainer ring. However, the problems were not fully solved because the rings remained vulnerable to being dislodged and coming loose. In U.S. Pat. No. 3,289,726 the grommet is exposed on one side of the panel when the fastener is separated. In U.S. Pat. No. 3,765,465 the grommet is secured to the panel, but the retainer ring is positioned within the opening in the panel so that the diameter of the opening must be relatively large. Increasing the dimension of the ring, in width or thickness, in an effort to improve its retention, has the disadvantage of increasing the inward spring force. This makes it difficult to advance the nut and results in excessive wear on the cadmium plating or other protective coating on the nut. Therefore, prior designs have represented a compromise rather than being fully staisfactory in all respects.